I wanted to give you a little blog post about preparing images for print. Based on whether the image is destined for a newspaper or a magazine, the resolution needs to be adjusted so the proper amount of ink is applied for the substrate used. Because the paper used for newsprint is more porous, there is more dot gain and less ink should be used. Magazines typically use a glossy paper and more ink is used. The image resolution for newspaper is 200 dpi and magazines is 300. Let’s take a look at the steps for preparing the image for each formats. For this example, the space I have to work with in my InDesign document is 6 3/8 x 6 3/4 inches. If I open the original image in Photoshop, you can see it is 14.4 w x 21.6 h at 240 ppi resolution.
We first need to change the resolution from 240 to 300 since this is going to be printed on glossy paper for our magazine. In Photoshop, go to the Image Size window, which can be found under the Image tab, uncheck the Resample Image, change the resolution to 300, and hit okay.
Now open the Image Size window again and click on the Resample Image box. Since we know we will want to keep the full width of the image, we will enter 6.375 in the width field of the document size. Make sure the chain link is activated so that the height adjusts proportionately along with the width. Notice the pixel dimension width is now 1913 pixels. Hit okay.
We know we are going to have to crop some of the image away. With the rectangle marquee tool selected, you can enter the pixel width and height of your image frame in the control panel. Click on the image and you will get a marquee box the size you need for your document. Place the box where you want and fom the tool bar, click on image, and then click crop.
With your image selected, you can check the Info Panel to make sure that your Actual PPI and Effective PPI are now in agreement and your image dimensions now say 1912 px wide by 2025 px high.
Like I said before, the difference between resolution for magazine and newspaper lies in the dot gain of the substrate. Because the paper used for newspapers is more porous, the resolution for images for newsprint is 200 dpi. Using the same process as above, you will go into the Image Size window, uncheck Resample Image, change the resolution to 200 and hit okay. Go back into the Image Size window, check Resample Image, and change the image size width to 6.375 inches. The height will scale proportionately to 6.75. After you place the image into the frame in your InDesign document, you will note in the Link Info panel the new pixel dimension and actual and effective PPI are in agreement for newspaper resolution.
Now you give it a try!